Fire retardant composition

ABSTRACT

A fire retardant composition comprising an alcohol deactivated solution of chlorosulfonic acid and digested plant material.

This is a continuation of application Ser. No. 626,253, filed Oct. 28,1975, now abandoned.

This invention relates to compositions for imparting fire resistance toand for fireproofing cellulosic materials, and further provides asimplified process for reducing the combustibility of normallycombustible materials.

More particularly, the present invention is directed to fire resistantcellulosic materials and a process for their preparation includingapplication of a treating agent, produced through alcoholic deactivationof a solution of chlorosulfonic acid digested plant material, to acellulosic substrate.

This invention is of particular significance because of the high rate ofutilization, particularly in the field of construction of cellulosic orwood materials. Simple and effective means for safeguarding the publicagainst the danger of fires attendant to these combustible materialshave long been sought. Therefore, the present process and products areof considerable importance insofar as they reduce the combustibility ofcellulosic materials through application of the present treating agent.

The treating agent used in accordance with the present inventioncomprises an alcohol deactivated solution of chlorosulfonic aciddigested plant material. Customarily, production of the present agentcomprises a two-step process. Firstly, a plant material, commonly wood,is digested in chlorosulfonic acid. Incident to digestion, thecellulose, lignin, and other constituents of the plant material aresolubilized in the acid. Thereafter, the solution containing plantmaterial is treated with alcohol to decompose the remainingchlorosulfonic acid, thus yielding a treating solution which isdeactivated with regard to its ability to digest cellulose.

During the first digestion step in the production of the treating agent,broad latitude is permitted in the selection of suitable proportions ofplant material and chlorosulfonic acid. Obviously, however, whenextremely low proportions of plant material are utilized, the resultant,intermediate solution will be dilute. Further, at the highestproportions of plant materials, complete digestion may not occur. Theforegoing drawbacks are not unduly limitative of the scope of thepresent invention, however, inasmuch as where the treating agent isdilute, higher proportions thereof may be employed in obtaining adequatefire retardance, and where all the plant material is not digested, theresultant slurry may still be utilized in accordance with the presentinvention, although, it is preferred that the solution be decanted, orfiltered, from its remaining solid constituents. It is preferred,however, that the plant material be present in an amount of from 1 to20%, most preferably 4 to 12% by weight of chlorosulfonic acid. Suitableconditions of digestion may also be varied greatly. Although ambienttemperatures are most convenient, higher or lower ones may be utilized.

In a preferred embodiment of the present invention, however, thecellulosic material is dried prior to exposure to the acid. Thus, forexample, it may be exposed to a temperature of from about 50° to 150° C.for at least 15 minutes. Pursuant thereto, excess water is removed so asto minimize the degree to which it will decompose the chlorosulfonicacid digesting agent.

The second step of deactivation of the chlorosulfonic acid solution ofdigested cellulosic material is somewhat more critical. Essentially,this second step proceeds in accordance with the following reaction:

    C.sub.n H.sub.2n+1 OH+ClSO.sub.2 OH→C.sub.n H.sub.2n+1 O--SO.sub.2 OH+HCl

The criticality of this step resides in the elimination ofchlorosulfonic acid from the eventual treating agent. Thus, an excess ofalcohol for decomposing the chlorosulfonic acid is permissible althoughit will dilute the eventual treating agent. Care should be taken,however, to ensure essentially complete decomposition as otherwise,application of the treating agent to the eventual cellulosic substratesought to be rendered fire retardant may result in some digestionthereof. Thus, it is preferred that the deactivating alcohol andchlorosulfonic acid remaining after digestion be reacted to inactivatethe chlorosulfonic acid.

In performing this deactivation, essentially any alcohol may beutilized. Preferably, however, the alcohol is selected from the loweralkyl alcohols of from 1 to 4 carbons such as methanol, ethanol,isopropanol, etc. The deactivation itself proceeds readily under ambientconditions upon addition of the alcohol to the solution and, at least inthe case of methanol, or isopropanol care should be taken to avoidunduly violent reaction incident to the decomposition of thechlorosulfonic acid. Thus, for example, the alcohol is usually addedrelatively slowly, with stirring, to the chlorosulfonic acid solutionand the reaction mixture may even be cooled during addition.

Once the treating agent has been produced, its application to thecellulosic substrate may be performed by any of the means customary inthe art. Thus, for example, the agent may be sprayed or painted onto thesurface of the substrate to provide a fire retardant film thereon.Alternatively, the substrate may be submerged or dipped into a bath ofthe agent to impregnate and/or coat the substrate. Obviously too, thedepth of impregnation and/or thickness of the coating film may easily bevaried to provide greater or lesser degrees of fire retardancy, asdesired.

Cellulosic substrates usefully treated in accordance with the presentinvention include any of the normally combustible cellulosic materialswell known in commerce in the prior art. By the expression "cellulosicsubstrate" in the following specification, it is meant, any articlewhich contains cellulose or a derivative thereof. Thus, for example, theterm embraces hemicellulose and other essentially carbohydrate polymerscontaining glucose or glucose derivative units. Particularly, however,this term is inclusive of the woody materials commonly employed asstructural members in the construction art; lumber, particleboard, cork,and other building materials are particularly useful in accordance withthe present invention.

Upon contact between the present cellulosic substrate and treatingagent, a darkened appearance is imparted to the substrate and it appearsthat some carbonization of the substrate surface occurs. Inasmuch as thealcoholically deactivated chlorosulfonic acid solution of plant materialis itself dark in color, it is unknown whether the appearance impartedto the substrate actually evidences a chemical reaction between thetreating agent and the substrate itself or is merely that of thetreating agent. Whatever does occur, however, the fire retardance isproduced.

In a further embodiment of the present invention the substrate andapplied treating agent may be dried to facilitate handling of the finalproduct. This step is easily accomplished by subjecting the composite toa short exposure to higher temperatures of the order of, for example,50° to 150° C. and ensures adherence of the treating agent to thesubstrate.

Further embodiments within the scope of the invention include additionalprecautionary steps to avoid loss of the treating agent from thesubstrate. Thus, for example, a protective coating of a paint, or othercovering materials as are known in the art may be applied to the surfaceof the substrate so as to ensure the permanency of the fire retardance.At the same time, such a protective step may have the additionaladvantage, particularly where it is in the form of a paint or otheropaque coating, of covering the substrate and thereby rendering theappearance of the product article more acceptable.

The invention is further illustrated by the following examples.

EXAMPLE 1

60 grams of Douglas-Fir wood flakes are dried for one hour at 100° C.and then added to 85 grams of chlorosulfonic acid. This slurry isallowed to digest for one hour at 23° C. during which essentially all ofthe wood is dissolved. The solution is then filtered and 170 grams ofisopropyl alcohol is added slowly to decompose the remainingchlorosulfonic acid, and to form a fire retardancy imparting treatingsolution.

Dry fir wood chips are then submerged in the treating solution for 2minutes before being removed and dried at 100° C. for 15 minutes. Uponbeing inserted in the flame of a Bunsen burner, these treated chipsexhibit only a slow smouldering of the wood in the flame area; no flamedevelops. After removal from the flame, only minor charring of the chipsurface is observed. In contrast to the foregoing, however, untreatedfir chips which were heated in the same manner burst into flame andcontinued to burn until they were converted to ash.

I claim:
 1. A composition for imparting fire retardance to a cellulosicsubstrate consisting of a substantially anhydrous solution of theproducts obtained by reacting the solution formed by digesting a mixtureconsisting of a dry plant material and chlorosulfonic acid with a loweralkyl alcohol in an amount at least sufficient to deactivate excess ofsaid acid.
 2. A fire retardance-imparting composition of claim 1,wherein said alcohol has from 1 to 4 carbons.